Modified support materials for catalysts

ABSTRACT

The present invention relates to a method of producing a catalyst or pre-catalyst suitable for assisting in the production of alkenyl alkanoates. The method includes contacting a modifier precursor to a support material to form a modified support material. One or more catalytic component precursors (palladium or gold) may be contacted to the modified support material. The atomic ratio of gold to palladium is preferably in the range of about 0.3 to about 0.90. The support materials with the catalytic component may then be reduced using a reducing environment. A composition for catalyzing the production of an alkenyl alkanoates including a modified support material with palladium and gold is also included within the invention. Catalysts of the present invention may be used to produce alkenyl alkanoates in general and vinyl acetate in particular and are useful to produce low EA/VA ratios while maintaining or improving CO 2  selectivity.

CLAIM OF PRIORITY

The application is a divisional of U.S. patent application Ser. No.11/285,436, filed on Nov. 21, 2005, which in turn claims the benefit ofU.S. application Ser. No. 60/637,529, filed on Dec. 20, 2004, which ishereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to catalysts, methods of making thecatalysts, and methods of making alkenyl alkanoates. More particularly,the invention relates to catalysts, methods of making the catalysts, andmethods of making vinyl acetate.

BACKGROUND OF THE INVENTION

Certain alkenyl alkanoates, such as vinyl acetate (VA), are commoditychemicals in high demand in their monomer form. For example, VA is usedto make polyvinyl acetate (PVAc), which is used commonly for adhesives,and accounts for a large portion of VA use. Other uses for VA includedpolyvinyl alcohol (PVOH), ethylene vinyl acetate (EVA), vinyl acetateethylene (VAE), polyvinyl butyral (PVB), ethylene vinyl alcohol (EVOH),polyvinyl formal (PVF), and vinyl chloride-vinyl acetate copolymer. PVOHis typically used for textiles, films, adhesives, and photosensitivecoatings. Films and wire and cable insulation often employ EVA in someproportion. Major applications for vinyl chloride-vinyl acetatecopolymer include coatings, paints, and adhesives often employ VAEhaving VA in some proportion. VAE, which contains more than 50 percentVA, is primarily used as cement additives, paints, and adhesives. PVB ismainly used for under layer in laminated screens, coatings, and inks.EVOH is used for barrier films and engineering polymers. PVF is used forwire enamel and magnetic tape.

Because VA is the basis for so many commercially significant materialsand products, the demand for VA is large, and VA production isfrequently done on a relatively large scale, e.g. 50,000 metric tons ormore per year. This large scale production means that significanteconomies of scale are possible and relatively subtle changes in theprocess, process conditions or catalyst characteristics can have asignificant economic impact on the cost of the production of VA.

Many techniques have been reported for the production of alkenylalkanoates. For example, in making VA, a widely used technique includesa catalyzed gas phase reaction of ethylene with acetic acid and oxygen,as seen in the following reaction:

C₂H₄+CH₃COOH+0.5O₂→CH₃COOCH═CH₂+HO

Several side reactions may take place, including, such as, the formationof CO₂. The results of this reaction are discussed in terms of thespace-time yield (STY) of the reaction system, where the STY is thegrams of VA produced per liter of catalyst per hour of reaction time(g/l*h).

The composition of the starting material feed can be varied within widelimits. Typically, the starting material feed includes 30-70% ethylene,10-30% acetic acid and 4-16% oxygen. The feed may also include inertmaterials such as CO₂, nitrogen, methane, ethane, propane, argon and/orhelium. The primary restriction on feed composition is the oxygen levelin the effluent stream exiting the reactor must be sufficiently low suchthat the stream is outside the flammability zone. The oxygen level inthe effluent is affected by the oxygen level in the starting materialstream, O₂ conversion rate of the reaction and the amount of any inertmaterial in the effluent.

The gas phase reaction has been carried out where a feed of the startingmaterials is passed over or through fixed bed reactors. Successfulresults have been obtained through the use of reaction temperatures inthe range of 125° C. to 200° C., while reaction pressures of 1-15atmospheres are typical.

While these systems have provided adequate yields, there continues to bea need for reduced production of by-products, higher rates of VA output,and lower energy use during production. One approach is to improvecatalyst characteristics, particularly as to CO₂ selectivity and/oractivity of the catalyst. Another approach is to modify reactionconditions, such as the ratio of starting materials to each other, theO₂ conversion of the reaction, the space velocity (SV) of the startingmaterial feed, and operating temperatures and pressures.

The formation of CO₂ is one aspect which may be reduced through the useof improved catalysts. The CO₂ selectivity is the percentage of theethylene converted that goes to CO₂. Decreasing the CO₂ selectivitypermits a larger amount of VA per unit volume and unit time in existingplants, even retaining all other reaction conditions.

The formation of ethyl acetate (EA) is another aspect which may bereduced through the use of improved catalysts. The EA selectivity isusually expressed in ppm as the ratio EA/VA wt/wt. Decreasing the EAselectivity permits reducing or eliminating post-production purificationof VA. By reducing the EA selectivity of a catalyst, the processingsteps associated with EA removal could be eliminated, thus providingcost savings. It would be desirable to achieve an EA/VA ratio less thanthe typical ratio of about 700 ppm, preferably less than about 200 ppmwithout sacrificing the catalysts' CO₂ selectivity or its activity.

Attempts to reduce EA output have included increasing the gold topalladium ratio on the catalyst, such as shown in U.S. Pat. No.5,185,308. While this patent indicates that the EA/VA ratio eventuallygoes to zero with a high enough gold to palladium ratio, experimentaltesting has been unable to reproduce this result. Furthermore, CO₂selectivity is sacrificed through the use of an increased gold topalladium ratio. Consequently, another approach is needed.

VA output of a particular reaction system is affected by several otherfactors including the activity of the catalyst, the ratio of startingmaterials to each other, the O₂ conversion of the reaction, the spacevelocity (SV) of the starting material feed, and operating temperaturesand pressures. All these factors cooperate to determine the space-timeyield (STY) of the reaction system, where the STY is discussed in termsof grams of VA produced per liter of catalyst per hour of reaction timeor g/l*h.

Generally, activity is a significant factor in determining the STY, butother factors may still have a significant impact on the STY. Typically,the higher the activity of a catalyst, the higher the STY the catalystis able to produce.

The O₂ conversion is a measure of how much oxygen reacts in the presenceof the catalyst. The O₂ conversion rate is temperature dependent suchthat the conversion rate generally climbs with the reaction temperature.However, the CO₂ selectivity also increases along with the increase intemperature. Thus, the O₂ conversion rate is selected to give thedesired VA output balanced against the amount of CO₂ produced. Acatalyst with a higher activity means that the overall reactiontemperature can be lowered while maintaining the same O₂ conversion.Alternatively, a catalyst with a higher activity will give a higher O₂conversion rate at a given temperature and space velocity.

It is common that catalysts employ one or more catalytic componentscarried on a relatively inert support material. In the case of VAcatalysts, the catalytic components are typically a mixture of metalsthat may be distributed uniformly throughout the support material (“allthrough-out catalysts”), just on the surface of the support material(“shell catalysts”), just below a shell of support material (“egg whitecatalysts”) or in the core of the support material (“egg yolkcatalysts”). Preferred type of metal distribution is dependent a numberof factors including the reactor system and catalyst size/shape.

Numerous different types of support materials have been suggested foruse in VA catalyst including silica, cerium doped silica, alumina,titania, zirconia and oxide mixtures. But very little investigation ofthe differences between the support materials has been done. For themost part, only silica and alumina have actually been commercialized assupport materials.

One useful combination of metals for VA catalysis is palladium and gold.Pd/Au catalysts provide adequate CO₂ selectivity and activity, but therecontinues to be a need for improved catalysts given the economies ofscale that are possible in the production of VA.

One process for making Pd/Au catalysts typically includes the steps ofimpregnating the support with aqueous solutions of water-soluble saltsof palladium and gold; reacting the impregnated water-soluble salts withan appropriate alkaline compound e.g., sodium hydroxide, to precipitate(often called fixing) the metallic elements as water-insolublecompounds, e.g. the hydroxides; washing the fixed support material toremove un-fixed compounds and to otherwise cleanse the catalyst of anypotential poisons, e.g. chloride; reducing the water insoluble compoundswith a typical reductant such as hydrogen, ethylene or hydrazine, andadding an alkali metal compound such as potassium or sodium acetate.

Various modifications to this basic process have been suggested. Forexample, in U.S. Pat. No. 5,990,344, it is suggested that sintering ofthe palladium be undertaken after the reduction to its free metal form.In U.S. Pat. No. 6,022,823, it suggested that calcining the support in anon-reducing atmosphere after impregnation with both palladium and goldsalts might be advantageous. In WO94/21374, it is suggested that afterreduction and activation, but before its first use, the catalyst may bepretreated by successive heating in oxidizing, inert, and reducingatmospheres.

In U.S. Pat. No. 5,466,652, it is suggested that salts of palladium andgold that are hydroxyl-, halide- and barium-free and soluble in aceticacid may be useful to impregnate the support material. A similarsuggestion is made in U.S. Pat. No. 4,902,823, i.e. use of halide- andsulfur-free salts and complexes of palladium soluble in unsubstitutedcarboxylic acids having two to ten carbons.

In U.S. Pat. No. 6,486,370, it suggested that a layered catalyst may beused in a dehydrogenation process where the inner layer support materialdiffers from the outer layer support material. Similarly, U.S. Pat. No.5,935,889 suggests that a layered catalyst may useful as acid catalysts.But neither suggests the use of layered catalysts in the production ofalkenyl alkanoates. In U.S. Patent Publication 2005/0181940, layeredcatalysts for vinyl acetate are shown, but modified support materialsare not.

In U.S. Pat. No. 5,808,136 it suggested that a titanium or zirconium maybe used to pre-treat a silica or alumina support material to improvedactivity and/or CO₂ selectivity of the catalyst.

Taken together, the inventors have recognized and addressed the need forcontinued improvements in the field of VA catalysts to provide improvedVA production at lower costs.

SUMMARY OF THE INVENTION

The present invention relates to a method of producing a catalyst orpre-catalyst suitable for assisting in the production of alkenylalkanoates. The method includes contacting a modifier precursor to asupport material to form a modified support material. One or morecatalytic component precursors (palladium and/or gold) may be contactedto the modified support material. The atomic ratio of gold to palladiumis preferably in the range of about 0.3 to about 0.90. The supportmaterials with the catalytic component may then be reduced using areducing environment and/or activated using with an activating agentsuch as KOAc. A composition for catalyzing the production of an alkenylalkanoates including a modified support material with palladium and goldis also included within the invention. Catalysts of the presentinvention may be used to produce alkenyl alkanoates in general and vinylacetate in particular.

DETAILED DESCRIPTION

Catalysts

For present purposes, a catalyst is any support material that containsat least one catalytic component and that is capable of catalyzing areaction, whereas a pre-catalyst is any material that results from anyof the catalyst preparation steps discussed herein.

Catalysts and pre-catalysts of the present invention may include thosehaving a modified support material. Effective use of the catalystaccordingly should help improve EA selectivity while maintaining orimproving CO₂ selectivity, activity or both, particularly as pertainingto VA production. Moreover, the combination of improving EA selectivelywhile maintaining or improving CO₂ selectivity may be desirable even ifactivity is adversely affected.

It should be appreciated that the present invention is described in thecontext of certain illustrative embodiments, but may be varied in any ofa number of aspects depending on the needs of a particular application.By way of example, without limitation, the catalysts may have thecatalytic components uniformly distributed throughout the supportmaterial or they may be shell catalysts where the catalytic componentsare found in a relatively thin shell around a support material core. Eggwhite catalysts may also be suitable, where the catalytic componentsreside substantially away from the center of support material. Egg yolkcatalysts may also be suitable. Preferred type of metal distribution isdependent on a number of factors including the reactor system andcatalyst size/shape and include shell catalysts and layered catalysts.

Catalytic Components

In general, the catalysts and pre-catalysts of the present inventioninclude metals and particularly include a combination of at least twometals. In particular, the combination of metals includes at least onefrom Group VIIIB and at least one from Group IB. It will be appreciatedthat “catalytic component” is used to signify the metal that ultimatelyprovides catalytic functionally to the catalyst, but also includes themetal in a variety of states, such as salt, solution, sol-gel,suspensions, colloidal suspensions, free metal, alloy, or combinationsthereof. Preferred catalysts include palladium and gold as the catalyticcomponents.

Another preferred embodiment of the catalyst includes between about 1 toabout 10 grams of palladium and preferably between about 1 and 10 gramsof palladium per liter.

In one embodiment for catalysts, Au to Pd atomic ratios between about0.1 and about 1.25 may be preferred for catalysts. Most preferred Au:Pdatomic ratios are from 0.3-0.9. The atomic ratio can be adjusted tobalance the EA/VA selectivity and CO₂ selectivity. Employment of higherAu/Pd weight or atomic ratios tends to favor relatively lower EA/VAratios but higher CO₂ selectivity.

One embodiment is the use of ground or powder catalysts for screening ofcatalyst compositions. A ground catalyst may be one where the catalyticcomponents are contacted to the support material followed by a reductionin the particle size (e.g. by grinding or ball milling) or one where thecatalytic components are contacted to the support material after thesupport material has been reduced in size. In one embodiment, a groundor powder catalyst is used to simulate a shell catalyst. In simulatedshell catalyst, an aliquot of support material with a relatively highconcentration of modifiers and/or catalytic components is diluted with asupport material that is substantially free of modifiers and/orcatalytic component, but has been activated with an activation agent(e.g. potassium acetate), as discussed below. The diluted supportmaterial then has the preferred amounts of modifiers and/or catalyticcomponents in the catalyst.

For shell catalysts, the thickness of the shell of catalytic componentson the support material ranges from about 5 μm to about 500 μm. Morepreferred ranges include from about 5 μm to about 300 μm.

Support Materials

In one aspect of the invention, the catalytic components of the presentinvention generally will be carried by a support material. Suitablesupport materials typically include materials that are substantiallyuniform in identity or a mixture of materials. Overall, the supportmaterials are typically inert in the reaction being performed. Supportmaterials may be composed of any suitable substance preferably selectedso that the support materials have a relatively high surface area perunit mass or volume, such as a porous structure, a molecular sievestructure, a honeycomb structure, or other suitable structure. Forexample, the support material may contain silica, alumina,silica-alumina, titania, titano-silicate, zirconia, zircono-silicate,niobia, silicates, alumino-silicates, titanates, spinel, siliconcarbide, silicon nitride, carbon, cordierite, steatite, bentonite,clays, metals, glasses, quartz, pumice, zeolites, non-zeolitic molecularsieves combinations thereof and the like. Any of the differentcrystalline form of the materials may also be suitable, e.g. alpha orgamma alumina. Zirconia, zircono-silicates and titano-silicatescontaining support materials are the most preferred. In addition,multilayer support materials are also suitable for use in the presentinvention.

The support material in the catalyst of this invention may be composedof particles having any of various regular or irregular shapes, such asspheres, tablets, cylinders, discs, rings, stars, or other shapes. Thesupport material may have dimensions such as diameter, length or widthof about 1 to about 10 mm, preferably about 3 to about 9 mm. Inparticular having a regular shape (e.g. spherical) will have as itspreferred largest dimension of about 4 mm to about 8 mm. In addition, aground or powder support material may be suitable such that the supportmaterial has a regular or irregular shape with a diameter of betweenabout 10 microns and about 1000 micron, with preferred sizes beingbetween about 10 and about 700 microns, with most preferred sizes beingbetween about 180 microns and about 450 microns. Larger or smaller sizesmay be employed, as well as polydisperse collections of particles sizes.For example, for a fluid bed catalyst a preferred size range wouldinclude 10 to 150 microns. For precursors used in layered catalysts, asize range of 10 to 250 microns is preferred.

Surface areas available for supporting catalytic components, as measuredby the BET (Brunauer, Emmett, and Teller) method, may generally bebetween about 1 m²/g and about 500 m²/g, preferably about 20 m²/g toabout 200 m²/g. For example, for a porous support, the pore volume ofthe support material may generally be about 0.1 to about 2 ml/g, andpreferably about 0.4 to about 1.2 ml/g. An average pore size in therange, for example, of about 50 to about 2000 angstroms is desirable,but not required.

Examples of suitable silica containing support materials include KA160from Sud Chemie, Aerolyst350 from Degussa and other pyrogenic ormicroporous-free silicas with a particle size of about 1 mm to about 10mm.

Examples of suitable zirconia containing support materials include thosefrom NorPro, Zirconia Sales (America), Inc., Daichi Kigenso KagakuKogyo, Engelhard and Magnesium Elektron Inc (MEI). Suitable zirconiasupport materials have a wide range of surface areas from less thanabout 5 m²/g to more than 300 m²/g. Preferred zirconia support materialshave surface areas from about 20 m²/g to about 150 m²/g, with a range ofbetween about 30 m²/g and about 100 m²/g more preferred. Supportmaterials may have their surfaces treated through a calcining step inwhich the virgin support material is heated. The heating reduces thesurface area of the support material (e.g. calcining). This provides amethod of creating support materials with specific surface areas thatmay not otherwise be readily available from suppliers.

Examples of other suitable support materials include titano-silicatesfrom Grace such as SP18-9534 (silica with 0.61% TiO₂) orzircono-silicates from Grace such as SP189043 (silica with 1.69% ZrO₂).More generally, suitable support materials may include up to about 50%TiO₂; more preferably between about 0.01% and about 25% TiO₂; and mostpreferably between about 0.1 and about 5% TiO₂. Also, suitable supportmaterials may include up to about 50% ZrO₂; more preferably betweenabout 0.01% and about 25% ZrO₂; and most preferably between about 0.1and about 5% ZrO₂.

In another embodiment, it is contemplated to employ at least a pluralcombination of support materials, each with a different characteristic.For example, at least two support materials (e.g. zirconia and silica)with different characteristics may exhibit different activities and CO₂selectivities, thus permitting preparation of catalysts with a desiredset of characteristics, i.e. activity of a catalyst may be balancedagainst the CO₂ selectivity of the catalyst.

Layered Support Materials

In one embodiment, plural different supports are employed in a layeredconfiguration as discussed in U.S. Patent Publication 2005/0181940,which is hereby incorporated by reference. Layering may be achieved inany of a number of different approaches, such as a plurality of lamellathat are generally flat, undulated or a combination thereof. Oneparticular approach is to utilize successively enveloping layersrelative to an initial core layer. In general, herein, layered supportmaterials typically include at least an inner layer and an outer layerat least partially surrounding the inner layer. All the layers of alayered catalyst may be modified as discussed below, with at least theouter layer preferably being modified. The outer layer also preferablycontains substantially more of catalytic components than the innerlayer. In one embodiment, the inner and outer layers are made ofdifferent materials; but the materials may be the same. While the innerlayer may be non-porous, other embodiments include an inner layer thatis porous.

The layered support material preferably results in a form of a shellcatalyst. But the layered support material offers a well definedboundary between the areas of the support material that have catalyticcomponents and the areas that do not. Also, the outer layer can beconstructed consistently with a desired thickness. Together the boundaryand the uniform thickness of the outer layer result in a shell catalystthat is a shell of catalytic components that is of a uniform and knownthickness.

Several techniques are known for creating layered support materialsincludes those described in U.S. Pat. Nos. 6,486,370; 5,935,889; and5,200,382, each of which is incorporated by reference. In oneembodiment, the materials of the inner layer are also not substantiallypenetrated by liquids, e.g., metals including but not limited toaluminum, titanium and zirconium. Examples of other materials for theinner layer include, but are not limited to, silica, alumina,silica-alumina, titania, titano-silicate, zirconia, zircono-silicate,niobia, silicates, alumino-silicates, titanates, spinel, siliconcarbide, silicon nitride, carbon, cordierite, steatite, bentonite,clays, metals, glasses, quartz, pumice, zeolites, non-zeolitic molecularsieves combinations thereof and the like. A preferred inner layer issilica and KA160, in particular.

These materials which make up the inner layer may be in a variety offorms such as regularly shaped particulates, irregularly shapedparticulates, pellets, discs, rings, stars, wagon wheels, honeycombs orother shaped bodies. A spherical particulate inner layer is preferred.The inner layer, whether spherical or not, has an effective diameter ofabout 0.02 mm to about 10.0 mm and preferably from about 0.04 mm toabout 8.0 mm.

The outermost layer of any multilayer structure is one which is porous,has a surface area in the range of about 5 m²/g to about 300 m²/g. Thematerial of the outer layer is a metal, ceramic, or a combinationthereof, and in one embodiment it is selected from alumina, silica,silica-alumina, titania, zirconia, niobia, silicates, aluminosilicates,titanates, spinel, silicon carbide, silicon nitride, carbon, cordierite,steatite, bentonite, clays, metals, glasses, quartz, pumice, zeolites,non-zeolitic molecular sieves and combinations thereof and preferablyinclude alumina, silica, silica/alumina, zeolites, non-zeolite molecularsieves (NZMS), titania, zirconia and mixtures thereof. Specific examplesinclude zirconia, silica and alumina or combinations thereof.

While the outer layer typically surrounds substantially the entire innerlayer, this is not necessarily the case and a selective coating on theinner layer by the outer layer may be employed.

The outer layer may be coated on to the underlying layer in a suitablemanner. In one embodiment, a slurry of the outer layer material isemployed. Coating of the inner layer with the slurry may be accomplishedby methods such as rolling, dipping, spraying, wash coating, otherslurry coating techniques, combinations thereof or the like. Onepreferred technique involves using a fixed or fluidized bed of innerlayer particles and spraying the slurry into the bed to coat theparticles evenly. The slurry may be applied repeatedly in small amounts,with intervening drying, to provide an outer layer that is highlyuniform in thickness.

The slurry utilized to coat the inner layer may also include any of anumber of additives such as a surfactant, an organic or inorganicbonding agent that aids in the adhesion of the outer layer to anunderlying layer, or combinations thereof. Examples of this organicbonding agent include but are not limited to PVA,hydroxypropylcellulose, methyl cellulose, and carboxymethylcellulose.The amount of organic bonding agent which is added to the slurry mayvary, such as from about 1 wt % to about 15 wt % of the combination ofouter layer and the bonding agent. Examples of inorganic bonding agentsare selected from an alumina bonding agent (e.g. Bohmite), a silicabonding agent (e.g. Ludox, Teos), zirconia bonding agent (e.g. zirconiaacetate or colloidal zirconia) or combinations thereof. Examples ofsilica bonding agents include silica sol and silica gel, while examplesof alumina bonding agents include alumina sol, bentonite, Bohmite, andaluminum nitrate. The amount of inorganic bonding agent may range fromabout 2 wt % to about 15 wt % of the combination of the outer layer andthe bonding agent. The thickness of the outer layer may range from about5 microns to about 500 microns and preferably between about 20 micronsand about 250 microns.

Once the inner layer is coated with the outer layer, the resultantlayered support will be dried, such as by heating at a temperature ofabout 100° C. to about 320° C. (e.g. for a time of about 1 to about 24hours) and then may optionally be calcined at a temperature of about300° C. to about 900° C. (e.g. for a time of about 0.5 to about 10hours) to enhance bonding the outer layer to it underlying layer over aleast a portion of its surface and provide a layered catalyst support.The drying and calcining steps can be combined into one step. Theresultant layered support material may be contacted with catalyticcomponents just as any other support material in the production ofcatalysts, as described below. Alternately, the outer layer supportmaterial is contacted to catalytic components before it is coated ontothe underlying layer.

In another embodiment of the layered support, a second outer layer isadded to surround the initial outer layer to form at least three layers.The material for the second outer layer may be the same or differentthan the first outer layer. Suitable materials include those discussedwith respect to the first outer layer. The method for applying thesecond outer layer may be the same or different than the method used toapply the middle layer and suitable methods include those discussed withrespect to the first outer layer. Organic or inorganic bonding agents asdescribed may suitably used in the formation of the second outer layer.

The initial outer layer may or may not contain catalytic components.Similarly, the second outer layer may or may not contain catalyticcomponents. If both outer layers contain catalytic component, thenpreferably different catalytic components are used in each layer,although this is not necessarily the case. In one preferred embodiment,the initial outer layer does not contain a catalytic component.Contacting catalytic component to the outer layers may be accomplishedby impregnation or spray coating, as described below.

In embodiments where the initial outer layer contains catalyticcomponent, one method of achieving this is to contact the catalyticcomponent to the material of the initial outer layer before the materialis applied to the inner layer. The second outer layer may be applied tothe initial outer layer neat or containing catalytic component.

Other suitable techniques may be used to achieve a three layered supportmaterial in which one or more of the outer layers contain catalyticcomponents. Indeed, the layered support material is not limited to threelayers, but may include four, five or more layers, some or all of whichmay contain catalytic components.

In addition, the number and type of catalytic components that varybetween the layers of the layered support material, othercharacteristics (e.g. porosity, particle size, surface area, porevolume, or the like) of the support material may vary between thelayers.

Modified Support Materials

In another embodiment, the support material may be a modified supportmaterial. A modified support material is one that includes a modifier.The modifier is preferably a metal selected from alkali metals, alkalineearth metals, transition metals, and lanthanides. More preferably themodifier is selected from group 1 to 6 elements. Of these elements,barium, magnesium, cerium, potassium, calcium, niobium, tantalum,titanium, yttrium, strontium, zirconium, lanthanum, praseodymium,vanadium, molybdenum, and rubidium are more preferred. Niobium,titanium, magnesium, and zirconium represent the preferred modifiers,with zirconium being slightly less preferred. Combinations of theseelements are also suitable with binary combinations the preferred typeof combination. For example, suitable binary combinations include Ti—Zr,Mg—Nb, Nb—Zr, Mg—Ti, Nb—Ti, Mg—Zr or the like. Ratios of metals in thebinary combinations range from about 4:1 to about 1:4.

Support materials are typically modified before catalytic components areadded to the support material. In one preferred embodiment, a supportmaterial is impregnated with one or more aqueous solution of themodifiers (referred to as modifier precursor solutions). The physicalstate of the support material during the contacting step may be a drysolid, a slurry, a sol-gel, a colloidal suspension or the like.

In one embodiment, the modifiers contained in the precursor solution arewater soluble salts made of the modifiers, including but not limited to,chlorides, other halides, nitrates, nitrites, hydroxides, oxides,oxalates, lactates, acetates (OAc), ammoniums and amines, with chloridefree salts being preferred, with lactates, oxalates and nitrates beingmost preferred. Examples of modifier salts suitable for use in modifierprecursor solutions include Ba(NO₃)₂, Mg(NO₃)₂.6H₂O, Ce(NO₃)₃.6H₂O,KNO₃, Ca(NO₃)₂.4H₂O, (NH₄)_(1.35)Nb(C₂O₄)_(2.73), Ta(C₂O₄)_(2.5),Ti(CH₃CH(O—)CO₂NH₄)₂(OH)₂, Y(NO₃)₃.6H₂O, ZrO(NO₃)₂.xH₂O.

Furthermore, more than one salt may be used in a given modifierprecursor solution. Precursor solutions typically may be made bydissolving the selected salt or salts in water, with or withoutsolubility modifiers such as acids, bases or other solvents. Othernon-aqueous solvents may also be suitable.

The modifier precursor solutions may be impregnated onto the supportmaterial in a single impregnation, although support materials maybeimpregnated multiple times with modifiers having low atomic weight (e.g.Mg) or limited solubility in water (e.g. Nb or Ba). If multiplemodifiers are utilized, the impregnation may be simultaneous (e.g.co-impregnation) or sequential and support material may be impregnatedthrough the use of one or multiple precursor solutions. Suitably, theamount of modifier impregnated on to the support material is betweenabout 0.01 wt % and about 5.0 wt % of the support material, andpreferably between about 0.1 wt % and about 4.0 wt %.

For the impregnating step, the volume of precursor solution may beselected so that it corresponds to up to about 110% of the pore volumeof the support material. Volumes between about 95% and about 100% of thepore volume of the support material are preferred

Typically, the modifier precursor solution is added to the supportmaterial and the support material is allowed absorb the precursorsolution. This may be done drop wise until incipient wetness of thesupport material is substantially achieved. Alternatively, the supportmaterial may be placed by aliquots or batch wise into the precursorsolution. A roto-immersion or other assistive apparatus may be used toachieve thorough contact between the support material and the precursorsolution. Further, a spray device may be used such that the precursorsolution is sprayed through a nozzle onto the support material, where itabsorbed. A fixing step is typically not used to fix the modifier on tothe support material, although this is not necessarily the case.

The modifier may be distributed all throughout the support material,distributed as a shell, and as an egg white or as an egg-yolk. Othercontacting techniques may be used. For example, modifiers may becontacted to a support material through a chemical vapor depositionprocess, such as described in US2001/0048970, which is incorporated byreference. Also, spray coating or otherwise layering a uniformlypre-impregnated support material, as an outer layer, on to an innerlayer may be suitable.

After the modifier precursor solution has been contacted to the supportmaterial, decanting, heat or reduced pressure may be used to remove anyexcess liquid not absorbed by the support material or to dry the supportmaterial.

After at least one modifier has been contacted to the support material,a calcining step may also be employed. The calcining step typically isbefore the catalytic components are contacted to the modified supportmaterial. The calcining step includes heating the support material in anon-reducing atmosphere (i.e. oxidizing or inert). During calcination,the modifiers on the support material are at least partially decomposedfrom their salts to a mixture of their oxide and free metal form.

For example, the calcining step is carried out at a temperature in therange of about 100° C. to about 900° C., preferably between about 300°C. and about 700° C. Non-reducing gases used for the calcination mayincluded one or more inert or oxidizing gases such as helium, nitrogen,argon, neon, nitrogen oxides, oxygen, air, carbon dioxide, combinationsthereof or the like. In one embodiment, the calcining step is carriedout in an atmosphere of substantially pure nitrogen, oxygen, air orcombinations thereof. Calcination times may vary but preferably arebetween about 1 and 5 hours. The degree of decomposition of the modifiersalts depends on the temperature used and length of time the modifiedsupport material is calcined and can be followed by monitoring volatiledecomposition products.

Methods of Making Catalysts

In general the method includes contacting modified support material withcatalytic components and reducing the catalytic components. Preferredmethods of the present invention include impregnating the catalyticcomponents into the support material, calcining the catalytic componentcontaining support material, reducing the catalytic components andactivating the reduced catalytic components on the support material.Additional steps such as fixing the catalytic components on the supportmaterial and washing the fixed catalytic components may also be includedin the method of making the catalyst or pre-catalyst. Some of the stepslisted above are optional and others may be eliminated (e.g. the washingand/fixing steps). In addition, some steps may be repeated (e.g.multiple impregnation or fix steps) and the order of the steps may bedifferent from that listed above (e.g. the reducing step precedes thecalcining step). To a certain extent, the contacting step will determinewhat later steps are needed for the formation of the catalyst.

Contacting Step

One particular approach to contacting is one pursuant to which an eggyolk catalyst or pre-catalyst is formed, an egg white catalyst orpre-catalyst is formed, an all throughout catalyst or pre-catalyst isformed or a shell catalyst or pre-catalyst is formed, or a combinationthereof. In one embodiment, techniques that form shell catalysts arepreferred.

The contacting step may be carried out using any of the modified supportmaterials described above, with niobium, titanium and magnesiummodifiers on support materials containing zirconia being the mostfavored. The contacting step is preferably carried out at ambienttemperature and pressure conditions; however, reduced or elevatedtemperatures or pressures may be employed.

In one preferred contacting step, a modified support material isimpregnated with one or more aqueous solutions of the catalyticcomponents (referred to as catalytic precursor solutions). The physicalstate of the support material during the contacting step may be a drysolid, a slurry, a sol-gel, a colloidal suspension or the like.

In one embodiment, the catalytic components contained in the precursorsolution are water soluble salts made of the catalytic components,including but not limited to, chlorides, other halides, nitrates,nitrites, hydroxides, oxides, oxalates, acetates (OAc), and amines, withhalide free salts being preferred and chloride free salts being morepreferred. Examples of palladium salts suitable for use in precursorsolutions include PdCl₂, Na₂PdCl₄, Pd(NH₃)₂(NO₂)₂, Pd(NH₃)₄(OH)₂,Pd(NH₃)₄(NO₃)₂, Pd(NO₃)₂, Pd(NH₃)₄(OAc)₂, Pd(NH₃)₂(OAc)₂, Pd(OAc)₂ inKOH and/or NMe₄OH and/or NaOH, Pd(NH₃)₄(HCO₃)₂ and palladium oxalate. Ofthe chloride-containing palladium precursors, Na₂PdCl₄ is mostpreferred. Of the chloride free palladium precursor salts, the followingfour are the most preferred: Pd(NH₃)₄(NO₃)₂, Pd(NO₃)₂, Pd(NH₃)₂(NO₂)₂,Pd(NH₃)₄(OH)₂. Examples of gold salts suitable for use in precursorsolution include AuCl₃, HAuCl₄, NaAuCl₄, KAuO₂, NaAuO₂, NMe₄AuO₂,Au(OAc)₃ in KOH and/or NMe₄OH as well as HAu(NO₃)₄ in nitric acid, withKAuO₂ being the most preferred of the chloride free gold precursors.

Furthermore, more than one salt may be used in a given precursorsolution. For example, a palladium salt may be combined with a gold saltor two different palladium salts may be combined together in a singleprecursor solution. Precursor solutions typically may be made bydissolving the selected salt or salts in water, with or withoutsolubility modifiers such as acids, bases or other solvents. Othernon-aqueous solvents may also be suitable.

The precursor solutions may be impregnated onto the support materialsimultaneously (e.g. co-impregnation) or sequentially and may beimpregnated through the use of one or multiple precursor solutions. Inaddition, a catalytic component may be impregnated on to supportmaterial in multiple steps, such that a portion of the catalyticcomponent is contacted each time. For example, one suitable protocol mayinclude impregnating with Pd, followed by impregnating with Au, followedby impregnating again with Au. In another protocol, Pd and Au arepreferably co-impregnated.

The order of impregnating the modified support material with thecatalytic precursor solutions is not critical; although there may besome advantages to certain orders, as discussed below, with respect tothe calcining step. Preferably, the palladium catalytic component isimpregnated onto the support material first, with gold being impregnatedafter palladium, or last. Also, the support material may be impregnatedmultiple times with the same catalytic component. For example, a portionof the overall gold contained in the catalyst may be first contacted,followed by contacting of a second portion of the gold. One more othersteps may intervene between the steps in which gold is contacted to thesupport material, e.g. calcining, reducing, and/or fixing.

The acid-base profile of the precursor solutions may influence whether aco-impregnation or a sequential impregnation is utilized. Thus, onlyprecursor solutions with similar acid-base profile should be usedtogether in a co-impregnating step; this eliminates any acid-basereactions that may foul the precursor solutions

For the impregnating step, the volume of precursor solution is selectedso that it corresponds to between about 85% and about 110% of the porevolume of the support material. Volumes between about 95% and about 100%of the pore volume of the support material are preferred. Further, forone step fixing and modifying discussed below, the modifier precursorsolution may make up a lower percentage of pore volume. For example,less than 50% of the pore volume, less than 25% of the pore volume orless than 10% of the pore volume.

Typically, the precursor solution is added to the support material andthe support material is allowed absorb the precursor solution. This maybe done drop wise until incipient wetness of the support material issubstantially achieved. Alternatively, the support material may beplaced by aliquots or batch wise into the precursor solution. Aroto-immersion or other assistive apparatus may be used to achievethorough contact between the support material and the precursorsolution. Further, a spray device may be used such that the precursorsolution is sprayed through a nozzle onto the support material, where itabsorbed. Optionally, decanting, heat or reduced pressure may be used toremove any excess liquid not absorbed by the support material or to drythe support material after impregnation.

Other contacting techniques may be used to avoid a fixing step whilestill achieving a shell catalyst. For example, catalytic components maybe contacted to a support material through a chemical vapor depositionprocess, such as described in US2001/0048970, which is incorporated byreference. Also, spray coating or otherwise layering a uniformlypre-impregnated support material, as an outer layer, on to an innerlayer effectively forms shell catalyst that may also be described as alayered support material. In another technique, organometallicprecursors of catalytic components, particularly with respect to gold,may be used to form shell catalysts, as described in U.S. Pat. No.5,700,753, which is incorporated by reference.

A physical shell formation technique may also be suitable for theproduction of shell catalysts. Here, the precursor solution may besprayed onto a heated modified support material or a layered modifiedsupport material, where the solvent of the precursor solution evaporatesupon contact with the heated support material, thus depositing thecatalytic components in a shell on the support material. Preferably,temperatures between about 40 and 140° C. may be used. Selecting thetemperature of the support material and the flow rate of the solutionthrough the spray nozzle may be used control the thickness of the shell.For example, with temperatures above about 100° C., a relatively thinshell is formed. This embodiment may be particularly useful whenchloride free precursors are utilized to help enhance the shellformation on the support material. See for example U.S. PatentPublication 20050181940.

One skilled in the art will understand that a combination of thecontacting steps may be an appropriate method of forming a contactedsupport material.

Fixing Step

It may be desirable to transform at least a portion of the catalyticcomponents on the contacted and modified support material from awater-soluble form to a water-insoluble form. Such a step may bereferred to as a fixing step. This may be accomplished by applying afixing agent (e.g. dispersion in a liquid, such as a solution) to theimpregnated support material which causes at least a portion of thecatalytic components to precipitate. This fixing step helps to form ashell catalyst, but is not required to form shell catalysts.

Any suitable fixing agent may be used, with hydroxides (e.g. alkalimetal hydroxides), silicates, borates, carbonates and bicarbonates inaqueous solutions being preferred. The preferred fixing agent is NaOH.Fixing may be accomplished by adding the fixing agent to the supportmaterial before, during or after the precursor solutions are impregnatedon the support material. Typically, the fixing agent is used subsequentto the contacting step such that the contacted support material isallowed to soak in the fixing agent solution for about 1 to about 24hours. The specific time depends upon the combination of the precursorsolution and the fixing agent. Like the impregnating step, an assistivedevice, such as a roto immersion apparatus as described in U.S. Pat. No.5,332,710, which is incorporated herein by reference, may advantageouslybe used in the fixing step.

The fixing step may be accomplished in one or multiple steps, referredas a co-fix or a separate fix. In a co-fix, one or more volumes of afixing agent solution is applied to the contacted support material afterall the relevant precursor solutions have been contacted to the supportmaterial, whether the contact was accomplished through the use of one ormultiple precursor solutions. For example, fixing after sequentialimpregnation with a palladium precursor solution and a gold precursorsolution would be a co-fix. An example of co-fixing may be found in U.S.Pat. No. 5,314,888, which is incorporated by reference.

A separate fix, on the other hand, would include applying a fixing agentsolution during or after each impregnation with a precursor solution.For example, the following protocols would be a separate fix: a)impregnating palladium followed by fixing followed by impregnating withgold followed by fixing; or b) co-impregnating with palladium followedby fixing followed by impregnating with gold followed by fixing. Betweena fix and subsequent impregnation, any excess liquid may be removed andthe support material dried, although this is not necessarily the case.An example of separate fixing may be found in U.S. Pat. No. 6,034,030,which is incorporated by reference.

In another embodiment, the fixing step and the contacting step areconducted simultaneously, one example of which is described in U.S. Pat.No. 4,048,096, which is incorporated by reference. For example, asimultaneous fix might be: impregnating with palladium followed byfixing followed by impregnating with gold and fixing agent. In avariation on this embodiment, the fix may be conducted twice for acatalytic component. A catalytic component may be partially fixed whenit is contacted to the support material (called a “pre-fix”), followedan additional, final fix. For example: impregnating with palladiumfollowed by impregnating with gold and a pre-fixing agent followed byfixing with a final fixing agent. This technique may be used to helpinsure the formation of shell type catalyst as opposed to an allthroughout catalyst.

In another embodiment of the simultaneous fixing and contacting step,the fixing solution is impregnated into the modified support materialsuch that between about 25 and about 95% of the pore volume is filled.Preferably, between about 70 and about 90% of the pore volume is filledby the fixing solution. The remainder of the pore volume is then filledwith the catalytic precursor solution. Step-wise or co-impregnation ofthe catalytic precursor may be used. This simultaneous fix andcontacting step avoids the need for a drying step, thus simplifying theprocess. Examples of fixing solutions include those comprising alkalimetal hydroxides, alkali metal carbonates, alkali metal bicarbonates ormixtures thereof. The fixing solutions may also be buffered to helpmaintain the pH of the solution.

In another embodiment, particularly suitable for use with chloride freeprecursors, the modified support material is pre-treated with a fixingagent to adjust the properties of the support material. In thisembodiment, the support material is first impregnated with either anacid or base solution, typically free of metals. After drying, thesupport material is impregnated with a precursor solution that has theopposite acidity/alkalinity as the dried support material. The ensuingacid-base reaction forms a shell of catalytic components on the supportmaterial. For example, nitric acid may be used to pre-treat a supportmaterial that in turn is impregnated with a basic precursor solutionsuch as Pd(OH)₂ or Au(OH)₃. This formation technique may be consideredas using a fixing step followed by a contacting step.

In another embodiment, the modified support may be pre-treated beforeimpregnation of the Pd and or Au in order to neutralize potentiallychemically reactive sites on the support material which may cause poorshell formation. For example, a basic support (e.g. zirconia) may bepre-treated with HCl to neutralize selected sites, followed by with Pdand Au impregnation and by fixing with base.

The concentration of fixing agent in the solution is typically a molarexcess of the amount of catalytic components impregnated on the supportmaterial. The amount of fixing agent should be between about 1.0 toabout 3.0, preferably about 1.1 to about 2.0 times the amount necessaryto react with the catalytically active cations present in thewater-soluble salt.

The volume of fixing agent solution supplied generally should be anamount sufficient to cover the available free surfaces of theimpregnated support material This may be accomplished by introducing,for example, a volume that is greater than the pore volume of thecontacted support material.

The combination of impregnating and fixing steps can form a shell typecatalyst. But, the use of halide free precursor solutions also permitsthe formation of a shell catalyst while optionally eliminating thefixing step. In the absence of a chloride precursor, a washing step, asdiscussed below, may be obviated. Further, the process can be free of astep of fixing catalytic components that would otherwise be needed tosurvive the washing step. Because no washing step is needed, thecatalytic components need not be fixed to survive the washing step.Subsequent steps in the method making the catalyst do not require thecatalytic components be fixed and thus the remainder of the step maybecarried out without additional preparatory steps. Overall, the use ofchloride free precursors permits a catalyst or pre-catalyst productionmethod that is free of a step of washing, thus reducing the number ofsteps needed to produce the catalyst and eliminating the need to disposeof chloride containing waste.

Washing Step

Particularly, when halide containing precursor solutions are utilizedand in other applications as desired, after the fixing step, the fixedsupport material may be washed to remove any halide residue on thesupport or otherwise treated to eliminate the potential negative effectof a contaminant on the support material. The washing step includedrinsing the fixed support material in water, preferably deionized water.Washing may be done in a batch or a continuous mode. Washing at roomtemperature should continue until the effluent wash water has a halideion content of less than about 1000 ppm, and more preferably until thefinal effluent gives a negative result to a silver nitrate test. Thewashing step may be carried out after or simultaneously with thereducing step, discussed below, but preferably is carried out before. Asdiscussed above, the use of halide free precursor solutions permits theelimination of the washing step.

Calcining Step of Catalytic Components

After at least one catalytic component has been contacted to the supportmaterial, one or more a calcining steps may be employed, although thisis not necessarily the case and in some instances is not preferred. Thecalcining step typically is before the reducing step and after thefixing step (if such a step is used) but may take place elsewhere in theprocess. In another embodiment, the calcining step is carried out afterthe reducing step. The calcining step includes heating the supportmaterial in a non-reducing atmosphere (i.e. oxidizing or inert). Duringcalcination, the catalytic components on the modified support materialare at least partially decomposed from their salts to a mixture of theiroxide and free metal form.

For example, the calcining step is carried out at a temperature in therange of about 100° C. to about 700° C., preferably between about 200°C. and about 500° C. Non-reducing gases used for the calcination mayincluded one or more inert or oxidizing gases such as helium, nitrogen,argon, neon, nitrogen oxides, oxygen, air, carbon dioxide, combinationsthereof or the like. In one embodiment, the calcining step is carriedout in an atmosphere of substantially pure nitrogen, oxygen, air orcombinations thereof. Calcination times may vary but preferably arebetween about 1 and 5 hours. The degree of decomposition of thecatalytic component salts depends on the temperature used and length oftime the impregnated catalyst is calcined and can be followed bymonitoring volatile decomposition products. Optionally, on zirconiasupport materials, only the Pd is calcined.

Reducing Step

Another step employed generally herein to at least partially transformany remaining catalytic components from a salt or oxide form to acatalytically active state, such as by a reducing step. Typically thisis done by exposure of salts or oxides to a reducing agent, examples ofwhich include ammonia, carbon monoxide, hydrogen, hydrocarbons, olefins,aldehydes, alcohols, hydrazine, primary amines, carboxylic acids,carboxylic acid salts, carboxylic acid esters and combinations thereof.Hydrogen, ethylene, propylene, alkaline hydrazine and alkalineformaldehyde and combinations thereof are preferred reducing agents withethylene and hydrogen blended with inert gases particularly preferred.Although reduction employing a gaseous environment is preferred, areducing step carried with a liquid environment may also be used (e.g.employing a reducing solution). The temperature selected for thereduction can range from ambient up to about 550° C. Reduction timeswill typically vary from about 1 to about 10 hours, with 5 hourspreferred.

Since the process used to reduce the catalytic components may influencesthe characteristics of the final catalyst, conditions employed for thereduction may be varied depending on whether high activity, highselectivity or some balance of these properties is desired.

In one embodiment, palladium is contacted to the support material, fixedand reduced before gold is contacted and reduced, as described in U.S.Pat. Nos. 6,486,093, 6,015,769 and related patents, all of which areincorporated by reference.

Exemplary protocols including a reducing step include: a) impregnatingwith palladium followed by optionally calcining followed by impregnatingwith gold followed by reducing; b) co-impregnating with palladium andgold followed by optionally calcining followed by reducing; or c)impregnating with palladium followed by optionally calcining followed byreducing followed by impregnating with gold.

Activating Step

Usually after the reducing step and before the catalyst is used, anactivating step is desirable. While the catalyst may be used without theactivating step, the step has several beneficial results, includinglengthening the operational life time of the catalyst. The activatingstep may be accomplished in accordance with conventional practice.Namely, the reduced support material is contacted with an activatingagent, such as an alkali metal salt (e.g. carboxylate and/or alkalimetal hydroxide), prior to use. Conventional alkali metal carboxylatessuch as the sodium, potassium, lithium and cesium salts of C₂₋₄aliphatic carboxylic acids are employed for this purpose. A preferredactivating agent in the production of VA is an alkali acetate, withpotassium acetate (KOAc) being the most preferred.

The support material may optionally be impregnated with a solution ofthe activating agent. After drying, the catalyst may contain, forexample, about 10 to about 70 grams, preferably about 20 to about 60grams of activating agent per liter of catalyst.

Methods of Making Alkenyl Alkanoates

The present invention may be utilized to produce alkenyl alkanoates froman alkene, alkanoic acid and an oxygen containing gas in the presence ofa catalyst. Preferred alkene starting materials contain from two to fourcarbon atoms (e.g. ethylene, propylene and n-butene). Preferred alkanoicacid starting materials used in the process of this invention forproducing alkenyl alkanoates contain from two to four carbon atoms(e.g., acetic, propionic and butyric acid). Preferred products of theprocess are VA, vinyl propionate, vinyl butyrate, and allyl acetate. Themost preferred starting materials are ethylene and acetic acid with theVA being the most preferred product. Thus, the present invention isuseful in the production of olefinically unsaturated carboxylic estersfrom an olefinically unsaturated compound, a carboxylic acid and oxygenin the presence of a catalyst. Although the rest of the specificationdiscusses VA exclusively, it should be understood that the catalysts,method of making the catalysts and production methods are equallyapplicable to other alkenyl alkanoates, and the description is notintended as limiting the application of the invention to VA.

When VA is produced using the catalyst of the present invention, astream of gas, which contains ethylene, oxygen or air, and acetic acidis passed over the catalyst. The composition of the gas stream can bevaried within wide limits, taking in account the zone of flammability ofthe effluent. For example, the molar ratio of ethylene to oxygen can beabout 80:20 to about 98:2, the molar ratio of acetic acid to ethylenecan be about 100:1 to about 1:100, preferably about 10:1 to 1:10, andmost preferably about 1:1 to about 1:8. The gas stream may also containgaseous alkali metal acetate and/or inert gases, such as nitrogen,carbon dioxide and/or saturated hydrocarbons. Reaction temperatureswhich can be used are elevated temperatures, preferably those in therange of about 125-220° C. The pressure employed can be a somewhatreduced pressure, normal pressure or elevated pressure, preferably apressure of up to about 20 atmospheres gauge.

In addition to fixed bed reactors, the methods of producing alkenylalkanoates and the catalyst of the present invention may also besuitably employed in other types of reaction, for example, fluidized bedreactors.

The methods of VA production preferably achieve an EA/VA ratio of lessthan about 800 ppm, more preferably less than about 400 ppm, morepreferably less than about 250 ppm and most preferably less than about200 ppm. The methods also preferably achieve a CO₂ selectivity of lessthan about 10%, and more preferably less than about 9% and mostpreferably less than 8% when the O₂ conversion is 45%. Most preferably,the catalyst will have both the EA/VA ratio and CO₂ selectivitydiscussed above.

Moreover, the present methods of VA production preferably result inmaintained or improved CO₂ selectivities as compared to a standardcatalyst utilized in similar processing conditions. A standard catalystis any catalyst that may be used as a control, and preferably does notinclude a modified support material. To make the comparison, thestandard catalyst is used as a control in the same or similar processingconditions as processing conditions for the modified support materialcatalyst. The catalyst on the modified support material need only match(or improve upon) the CO₂ selectivity of the standard catalyst at agiven O₂ conversion. One example of a catalyst that may be used as astandard catalyst is shown in U.S. Pat. No. 5,332,710, herebyincorporated by reference.

Examples of Catalysts on Modified Support Materials

Combinatorial/High Throughput chemistry and analysis techniques wereutilized to screen catalysts with modified support materials. Thecompositional space for the screened catalysts included those with goldand palladium as catalytic components where the atomic ratio of gold topalladium is between 0.3 to 1.2. Support materials included: KA-160(silica-alumina), Norpro XZ 16052 (zirconia), Aerolyst 350 (silica),Grace SP-9600 (silica), Grace SP-9601 (silica), Grace SP-9599 (silica),Grace SP-9602 (silica), Grace SP189043.USA3 (zircono-silica), GraceSP18-9534 (titano-silicate), Norpro XZ 16075 (zirconia) and Norpro XZ16052 (zirconia). The above support materials were modified with Ba, Mg,Ce, K, Ca, Nb, Ta, Ti, Y, Sr, Z, La, Pr, V, Mo, Rb, and selectedbimetallic combinations discussed above. Unmodified support materialswere also tested as controls.

Modified support materials other than zirconia were prepared byimpregnating 0.5 g samples of support (dried at 120° C. for at least 2h) to incipient wetness with modifier precursor solutions to achieve oneof three levels: 1.0, 2.0 and 4.0 wt %. This was followed by drying at105° C. for at least 2 h and calcination at 500° C., with 2° C./minheating rate. A robot from Hamilton was used to do all liquid dispensing

The modified support materials were impregnated to incipient wetnesswith a solution of Pd(NH₃)₄(OH)₂ to a Pd loading of 42.6 g Pd/Lcatalyst. During and after impregnation, the support materials werehomogenized for at least 1 h. After impregnation, the support materialswere dried in air at 105° C. for at least 2 h, and then calcined in airat 350° C. for 2 h, with a heating rate of 2° C./min.

Next, the modified support materials were impregnated to incipientwetness with freshly prepared 1 M [KOH+Au(OH)₃] solution to achieveAu:Pd ratios of 0.45, 0.6, 0.9, and 1.2. During and after impregnation,the impregnated support materials were homogenized for at least 1 h,followed by drying in air at 105° C. for at least 2 h.

The modified support materials with the catalytic components werereduced in 7% hydrogen in nitrogen. The samples were placed in smallcrucibles in which the catalyst bed was about 1 to 3 mm deep. A flow of100 mL was maintained throughout the reduction, with a 2° C./min heatingrate, 5 h at 350° C. After reduction, the samples were activated byimpregnation with a KOAc solution to 40 g KOAc/L catalyst and dried at105° C. for at least 2 h.

Modified zirconia support materials were made using essentially thatsame procedure as discussed above, except that no calcination took placeafter Pd impregnation and the reduction utilized 5% ethylene in nitrogenat 150° C.

Catalysts prepared according to this protocol were heterogeneouslydiluted with support material containing 40 g/l KOAc to give an overallPd loading of 7 g/l. The simulated shell catalysts were tested using astandard line-in protocol to test the catalysts' CO₂ selectivity andEA/VA ratios using a parallel reactor system. The standard protocolincluded testing the catalysts for 8 hours under normal feeds at 145° C.(13.8% HOAc, 40% C₂H₄, 7.9% O₂ and 38% N₂, P=10 atm, SV=138 cc/min/cccatalyst). A temperature ramp of 155° C., 165° C., 175° C. and 145° C.was then used to obtain information on each catalyst. Catalysts thatshowed CO₂ selectivity less than about 9.0% at 45% O₂ conversion and anEA/VA ratio of less than 800 ppm were deemed acceptable.

Catalysts on modified support materials that showed acceptable CO₂selectivity and EA/VA ratios are shown in the table below:

Support material Name Ta Nb Ti Y Zr Mg Pr La silica-alumina KA-160 x x xx x x zircono-silicate Grace SP189043.USA3 x x x silica Aerolyst 350 x xtitano-silicate Grace SP18-9534 x x x x silica Grace SP-9601 x x xzirconia Norpro XZ 16075 x x x x x x zirconia Norpro XZ 16052 x x x

Based on the results above, other levels of modifier (e.g. 0.1 wt % and0.4 wt %) and/or other Au:Pd ratios were tested to optimize the CO₂selectivity and the EA/VA ratio. Furthermore, variations in catalystpreparation conditions were also tested (e.g. different calcinationtemperatures, impregnation methods and/or different reductionconditions).

To differentiate between the acceptable catalysts, a high temperaturedeactivation test was used. Normal feeds (13.8% HOAc, 40% C₂H₄, 7.9% O₂and 38% N₂, P=10 atm, SV=138 cc/min/cc catalyst) were used for 8 hoursat 180° C. as a line-in protocol. The line-in was followed by atemperature ramp of 165° C., 175° C., 185° C., 195° C. and 165° C.Catalysts that showed acceptable properties under a more stringent setof guidelines (e.g. an EA/VA ratio of less than about 250 ppm withacceptable CO₂ selectivity at 45% O₂ conversion) would be the mostpreferred of the catalysts on the modified support materials. Under thisprotocol, the most preferred modified supports include niobium, titaniumand magnesium on zirconia support materials. Also preferred weretitanium and zirconium modifiers on the titano-silicate.

Comparison of catalysts with and without modified support materials maybe carried out using any VA synthetic procedure so long as the sameprocedure is used to test both types of catalysts. It will be furtherappreciated that functions or structures of a plurality of components orsteps may be combined into a single component or step, or the functionsor structures of one-step or component may be split among plural stepsor components. The present invention contemplates all of thesecombinations. Unless stated otherwise, dimensions and geometries of thevarious structures depicted herein are not intended to be restrictive ofthe invention, and other dimensions or geometries are possible. Pluralstructural components or steps can be provided by a single integratedstructure or step. Alternatively, a single integrated structure or stepmight be divided into separate plural components or steps. In addition,while a feature of the present invention may have been described in thecontext of only one of the illustrated embodiments, such feature may becombined with one or more other features of other embodiments, for anygiven application. It will also be appreciated from the above that thefabrication of the unique structures herein and the operation thereofalso constitute methods in accordance with the present invention.

The explanations and illustrations presented herein are intended toacquaint others skilled in the art with the invention, its principles,and its practical application. Those skilled in the art may adapt andapply the invention in its numerous forms, as may be best suited to therequirements of a particular use. Accordingly, the specific embodimentsof the present invention as set forth are not intended as beingexhaustive or limiting of the invention. The scope of the inventionshould, therefore, be determined not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. The disclosures of all articles and references,including patent applications and publications, are incorporated byreference for all purposes.

1. A method of producing a catalyst or pre-catalyst suitable forassisting in the production of alkenyl alkanoates, comprising:contacting a modifier precursor to a support material; contacting atleast one catalytic component precursor to the modified supportmaterial; and reducing the catalytic component precursor by contacting areducing environment to the support material.
 2. The method of claim 1further comprising calcining the modified support material in anon-reducing atmosphere prior to contacting the at least one catalyticcomponent precursor to the modified support material.
 3. The method ofclaim 2 wherein the modifier precursor comprises barium, magnesium,cerium, potassium, calcium, niobium, tantalum, titanium, yttrium,strontium, zirconium, lanthanum, praseodymium, vanadium, molybdenum,rubidium, or binary combinations thereof.
 4. The method of claim 3wherein the modifier precursor comprises niobium, titanium, magnesium,zirconium or combinations thereof.
 5. The method of claim 4 wherein themodifier precursor comprises niobium, titanium, magnesium orcombinations thereof.
 6. The method of claim 2 wherein the modifierprecursor comprises a chloride, a nitrate, an oxalate, a lactate orcombinations thereof.
 7. The method of claim 2 wherein the supportmaterial comprises zirconia.
 8. The method of claim 20 wherein thesupport material comprises titano-silicate or zircono silicate.
 9. Themethod of claim 2 wherein the support material is a layered supportmaterial.
 10. The method of claim 1 wherein the first contacting stepcomprises impregnating the support material with an aqueous modifierprecursor solution.
 11. The method of claim 10 wherein the firstcontacting step comprises contacting the support material with betweenabout 0.1 wt % and about 4.0 wt % of modifier based on the weight ofsupport material.
 12. The method of claim 1 wherein the secondcontacting step comprises impregnating the support material with anaqueous catalytic component precursor solution.
 13. The method of claim3 wherein the modifier calcining step comprises calcining at atemperature between about 300° C. and about 700° C.
 14. The method ofclaim 1 further comprising calcining after contacting the supportmaterial with the catalytic component precursor.
 15. The method of claim1 wherein the catalytic component precursor comprises gold, palladium,or a combination thereof.
 16. The method of claim 15 wherein the atomicratio of gold to palladium is between about 0.1 and about 1.25.
 17. Themethod of claim 16 wherein atomic ratio of gold to palladium is betweenabout 0.3 and about 0.90.
 18. The method of claim 1 further comprisingcontacting the catalyst or pre-catalyst with an activating agent. 19.The method of claim 18 further comprising contacting alkali metalacetate to the support material in an amount of between about 10 and 70grams per liter of catalyst.
 20. The method of claim 15 wherein thecatalytic component contacting step comprises contacting between about 1to about 10 grams of palladium per liter of catalyst, and about 0.5 toabout 10 grams of gold per liter of catalyst, with the amount of goldbeing from about 10 to about 125 wt % based on the weight of palladium.21. A composition for catalyzing the production of an alkenylalkanoates, comprising: a modified support material with at leastpalladium and gold contacted thereon to form a catalyst or pre-catalyst,wherein the modified support material is formed from one or moremodifier precursors.